Atomic Transport in Au-Ge Droplets: Brownian and Electromigration Dynamics

Diffusion, dissolution, and crystallization phenomena occurring in alloys at the liquid-solid interface are crucial in many contexts. To study these processes one approach consists in analyzing the fluctuation dynamics of the alloy or its response to a perturbation.

In this letter we use low-energy electron microscopy and atomic force microscopy to study atomic transport in Au-Ge droplets on Ge(111) substrate. We show that the Au-Ge droplets dig a hole into the substrate and drag it while randomly migrating or electromigrating under an applied electric current. The droplet motion is due to a mass transport phenomenon based on Ge dissolution at the droplet front and Ge crystallization at its rear. At high temperature the mass transport is limited by attachment or detachment at the solid-liquid interface with a constant activation energy whereas the low temperature regime is characterized by an activation energy that is droplet-size dependent. This result is assigned to a mechanism of 2D nucleation of layers at the liquid-solid interface.

Leroy, A. El Barraj, F. Cheynis, P. Müller, and S. Curiotto

PHYSICAL REVIEW LETTERS 123, 176101 (2019)